Embodiments of the disclosure pertain to methods, systems and apparatus for depositing transparent conductive oxide material on a substrate, such as a silicon wafer.
Transparent conductive oxides (TCO) are doped metal oxides used as transparent conducting layers in photovoltaic devices, such as solar cells. One method of depositing TCO material is referred to as reactive plasma deposition (RPD) in which a plasma gun generates a plasma beam that is guided toward a source via an electric magnetic field. The bombardment of the source with the plasma beam results in the source reaching its sublimation temperature. As a result the source material becomes vaporized and ionized before being deposited on the surface of a substrate within the chamber.
During the deposition process the ions and neutrals travel at various different angles (following a cosine distribution function) and may encounter and be deposited upon the sidewalls of the process chamber instead of the substrate. Any TCO material that is deposited on the sidewalls of the chamber results a loss of some ions and neutrals, which in turn represents a less than optimal use of the source (raw) material of the process.
The cost of producing products that include one or more thin film TCO layers deposited over a substrate, such as solar panels, in a commercial setting can be reduced by obtaining a high yield of the source material (i.e., the percentage of source material consumed is deposited on the substrate) as well as by depositing the source material on the substrate at a high deposition rate while ensuring relatively uniform deposition thickness across the substrate. Cost can also be reduced by reducing the overall footprint that deposition tools require within a fabrication facility so that more tools can fit within the facility in a given square foot area.